System and method for allocating a channel quality information channel in a communication system

ABSTRACT

A method for requesting allocation of a Channel Quality Information Channel (CQICH) by a Mobile Station (MS) in a communication system. The method includes switching, by the MS, from a serving anchor Base Station (BS) to a target anchor BS, detecting an absence of a CQICH allocated from the target anchor BS, and transmitting, from the MS to the target anchor BS, a CQICH allocation request. The CQICH allocation request includes a CQICH allocation request header including a basic Connection IDentifier (CID) of the MS and a Header Check Sequence (HCS) for the CQICH allocation request header.

PRIORITY

This application is a Divisional Application of U.S. application Ser.No. 11/328,828, which was filed in the U.S. Patent and Trademark Officeon Jan. 10, 2006, and claims priority under 35 U.S.C. §119 to anapplication filed in the Korean Intellectual Property Office on Jan. 10,2005 and assigned Serial No. 2005-2327, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a system and method forallocating a Channel Quality Information Channel (CQICH) in acommunication system.

2. Description of the Related Art

Active research on the next generation communication system is beingconducted to provide users with desired services which can meet adesired Quality-of-Service (QoS) at a high data rate.

A wireless Local Area Network (LAN) communication system and a wirelessMetropolitan Area Network (MAN) communication system support a high datarate. The wireless MAN communication system, one of the typicalBroadband Wireless Access (BWA) communication systems, has broaderservice coverage and supports a higher data rate, compared with thewireless LAN communication system. Therefore, active research on thenext generation communication system is being conducted to develop a newcommunication system that guarantees mobility of a mobile station (MS)and QoS to the wireless LAN communication system and the wireless MANcommunication system, both of which guarantee a higher data rate, tothereby support a higher data rate of the next generation communicationsystem.

A system employing an Orthogonal Frequency Division Multiplexing (OFDM)scheme and/or an Orthogonal Frequency Division Multiple Access (OFDMA)scheme to support a broadband transmission network for physical channelsof the wireless MAN communication system is known as an Institute ofElectrical and Electronics Engineers (IEEE) 802.16 communication system.The IEEE 802.16 communication system, applies the OFDM/OFDMA scheme tothe wireless MAN communication system, and can therefore supporthigh-speed data transmission by transmitting physical channel signalsusing a plurality of subcarriers. For convenience, the followingdescription will be made with reference to the IEEE 802.16 communicationsystem, one of the typical BWA communication systems.

A description will now be made of a Fast Base Station Switching (FBSS)scheme among various handover schemes for connection switching from aserving base station (BS) to a target BS in the IEEE 802.16communication system.

The FBSS scheme is a handover scheme that uses selection diversity andfast switching mechanism to improve link quality. In the FBSS scheme, amobile station (MS) exchanges signals with only one active BS, i.e., ananchor BS, among active BSs included in the MS's diversity set. Theanchor BS is a type of serving BS, and is replaceable (or switchable)according to a BS selection scheme of the MS. A description will now bemade of the diversity set.

Each of active BSs constituting the MS's diversity set is distinguishedwith a temporary BS indicator (Temp BS ID), and all of the active BSsconstituting the diversity set share capability, security parameters,service parameters, and full Medium Access Control (MAC) contextinformation of the corresponding MS. Each of the active BSs constitutingthe diversity set can be excluded from the diversity set or a new BScurrently not included in the diversity set can be added to thediversity set as a new active BS according to strength of a signalreceived (by the MS) from each active BS.

The MS selects one of the active BSs constituting the diversity set asan anchor BS. In this case, strength, for example,carrier-to-interference and noise ratio (CINR), of a signal receivedfrom the active BS selected as the anchor BS is highest, compared withCINRs of signals transmitted by the other active BSs constituting thediversity set. Therefore, in the FBSS scheme, the MS “performscommunication” with only the anchor BS. The anchor BS that currentlycommunicates with the MS will be referred to as a “serving anchor BS.”The MS measures signal quality for each of the active BSs constitutingthe diversity set while communicating with the serving anchor BS.Measuring the signal quality means measuring a CINR of the correspondingsignal. Upon detecting the presence of any active BS providing highersignal quality than that of the current serving anchor BS as a result ofthe signal quality measurement, the MS determines to handover from theserving anchor BS to the active BS that provides the higher signalquality than that of the current serving anchor BS, accomplishing fastswitching. Herein, an active BS, to which the MS performs fastswitching, that provides a higher signal quality than that of thecurrent serving anchor BS will be referred to as a “target anchor BS.”

With reference to FIG. 1, a description of an FBSS-based fast switchingoperation of an MS in a conventional IEEE 802.16 communication systemwill now be given. FIG. 1 is a flowchart illustrating an FBSS-based fastswitching operation of an MS in a conventional IEEE 802.16 communicationsystem.

Referring to FIG. 1, an MS performs communication with a serving anchorBS in step 101. Thereafter, the MS measures signal quality for eachactive BSs constituting the MS's diversity set in step 103. Herein, thephrase an MS performs communication with a serving anchor BS means thatallocation information for the MS is included in MAP messages, i.e., adownlink MAP (DL-MAP) message and an uplink MAP (UL-MAP) message,transmitted by the serving anchor BS.

The MS determines in step 105 whether it should switch the servinganchor BS, i.e., it should perform a fast switching operation. Herein,the MS determines to switch the serving anchor BS if there is any activeBS having a higher signal quality than that of the serving anchor BS. Ifthere is no need to switch the anchor BS as a result of thedetermination, the MS returns to step 101. However, if it is determinedin step 105 that there is a need to switch the anchor BS, the MSproceeds to step 107.

In step 107, the MS detects a start point of a switch period. Herein,the switch period refers to a period in which an MS reports a servinganchor BS that it will perform a fast switching operation to a newactive BS, i.e., a target anchor BS, rather than the serving anchor BS.The switch period will be described later in detail with reference toFIG. 2. In step 109, after detecting the start point of the switchperiod, the MS transmits a Temp BS ID of a target anchor BS to which itwill perform a fast switching operation from the serving anchor BS, tothe serving anchor BS in the switch period. Herein, the MS transmits theTemp BS ID of the target anchor BS (i.e., a codeword corresponding tothe Temp BS ID), to the serving anchor BS through a CQICH allocated fromthe serving anchor BS. The CQICH is a channel used by the MS to transmita control signal in a process of feeding back a Channel qualityinformation (CQI) value of the serving anchor BS or performing anFBSS-based fast switching operation.

Possible codewords mapped to corresponding Temp BS IDs are shown inTable 1 below.

TABLE 1 Value Description 0b100000 Active BS for TEMP_BS_ID = 0000b100001 Active BS for TEMP_BS_ID = 001 0b100010 Active BS forTEMP_BS_ID = 010 0b100011 Active BS for TEMP_BS_ID = 011 0b100100 ActiveBS for TEMP_BS_ID = 100 0b100101 Active BS for TEMP_BS_ID = 101 0b100110Active BS for TEMP_BS_ID = 110 0b100111 Active BS for TEMP_BS_ID = 1110b101000 Acknowledgement of Receipt of Anchor BS Switch IE

In Table 1, “Value” represents codewords mapped to corresponding Temp BSIDs of active BSs. For example, if the MS desires to perform fastswitching from a serving anchor BS to a target anchor BS with Temp BSID=“011”, the MS transmits a codeword “0b100011” mapped to the Temp BSID=‘011’ to the serving anchor BS through a CQICH. In Table 1, acodeword ‘0b101000’ is not a codeword mapped to a Temp BS ID of anactive BS, but is a codeword used by the serving anchor BS to inform theMS that it has received a transmitted anchor BS switch InformationElement (Anchor BS Switch IE). A format of the Anchor BS Switch IE willbe described later in detail.

In step 111, the MS transmits a CQI value for the serving anchor BSthrough a CQICH being identical to the CQICH used for transmitting acodeword mapped to the Temp BS ID of the target anchor BS. The MSdetermines in step 113 whether an Anchor BS Switch IE indicating a fastswitching cancel request to the target anchor BS is received from theserving anchor BS. A format of the Anchor BS Switch IE is shown in Table2.

TABLE 2 Syntax Size Notes Anchor BS Switch IE( ){ N_Anchor BS_Switch 4bits Number of Anchor BS switching for(i=0;i<N_Anchor indicated in thisIE BS_Switch;i++){  CID 16 bits  Basic CID of a MS whose anchor BSswitching is indicated in this IE  Action code 2 bits 00 - The MS shallswitch to the Anchor BS specified in the fast Anchor BS selectioninformation in the Fast-feedback channel, at the default time specifiedby the switching period defined in the DCD 01 - The MS shall switch tothe Anchor BS specified in this IE and at the action time specified inthis IE 10 - The MS shall cancel all anchor switching procedure, stopswitching timer and remain on the current anchor BS 11 - reserved  if(Action code ==01){   Action time(A) 3 bits In units of frames, 000means the MS shall switch at the default time specified by the switchingperiod defined in DCD   TEMP BS ID 3 bits TEMP BS ID of the anchor BS to } switch to.  If(Action code==00 || Action code==01){  CQICH Allocation1 bit To indicate if CQICH allocation at Indicator the new Anchor BS isincluded in this IE  if(CQICH Allocation Indicator ==1){   CQICH IDVariable Index to uniquely identify the CQICH resource assigned to theMS after the MS switched to the new Anchor BS   Feedback channel 6 bitsIndex to the Fast feedback channel offset region of the new Anchor BSmarked by UIUC = 0   Period(p) 2 bits A CQI feedback is transmitted onthe CQICH every 2^(p) frames   Frame offset 3 bits The MS startsreporting at the frame of which the number has the same 3 LSB as thespecified frame offset. If the current frame is specified, the MS shouldstart reporting in 8 frames.   Duration(d) 3 bits A CQI feedback istransmitted on the CQI channels indexed by the CQICH ID for frames if d= 0, the CQICH is deallocated if d = 111, the MS should report until theBS commend for the MS to stop   }  } }

In Table 2, N_Anchor BS_Switch represents the number of anchor BS fastswitching informations included in the Anchor BS Switch IE, and theAnchor BS Switch IE can include anchor BS fast switching informationsallocated to a plurality of MSs because it is included in a MAP messagebefore being broadcasted. Herein, the number of anchor BS fast switchinginformations is equivalent to “N_Anchor BS_Switch”, and each of “anchorBS fast switching informations” is equivalent to each of informations in“for (i=0; i<N_Anchor BS_Switch; i++)” structure. The Anchor BS SwitchIE includes a Connection Identifier (CID) for each of the anchor BS fastswitching informations, an Action code, and CQICH allocation informationfor the Action code. The CID represents a basic CID for each MS, and theAction code represents information on a switch period in which the MSfast-switches to the target anchor BS, or information used forcommanding the MS to fast-switch to a target anchor BS indicated by theserving anchor BS in a period (i.e., a switch period), indicated by theserving anchor BS, or for commending the MS to cancel the fastswitching.

As shown in Table 2, Action code=“00” indicates that the MS shouldperform a fast switching operation to the target anchor BS at a defaulttime in a switch period defined in a Downlink Channel Descriptor (DCD)message, Action code=‘01’ indicates that the MS should perform a fastswitching operation to the target anchor BS at an action time specifiedin the Anchor BS Switch IE, and Action code=‘10’ indicates that the MSshould cancel the fast switching operation and maintain communicationwith the serving anchor BS.

In Table 2, CQICH Allocation Indicator represents CQICH allocationinformation to be used by the MS in the target anchor BS. The CQICHallocation information includes CQICH ID, Feedback channel offsetindicating a position of a CQICH actually allocated to the MS in a CQIfield defined in a UL-MAP message, Period (p) indicating a period inwhich the MS reports a CQI value, Frame offset indicating a time atwhich the MS starts reporting a CQI value, and Duration (d) indicatinginformation on effective duration of a CQICH allocated from the targetanchor BS. Therefore, an MS, receiving the CQICH allocation information,reports a CQI value to the target anchor BS through the CQICH every2^(p) frame for frame duration after the Frame offset time.

If it is determined in step 113 that an Anchor BS Switch IE indicating afast switching cancel request to the target anchor BS is received fromthe serving anchor BS (i.e., the Action code is set to “10”), the MSproceeds to step 115. In step 115, the MS cancels a fast switchingoperation (from the serving anchor BS to the target anchor BS), and thenends the process.

However, if it is determined in step 113 that an Anchor BS Switch IEindicating a fast switching cancel request to the target anchor BS isnot received from the serving anchor BS, the MS proceeds to step 117where it determines whether the switch period has expired. If it isdetermined that the switch period has not expired, the MS returns tostep 109 where it can repeatedly transmit information indicating adesired fast switching operation to the target anchor BS (i.e., the MStransmits a codeword mapped to a Temp BS ID of the target anchor BS), tothe serving anchor BS. The repeated transmission of the codeword mappedto the Temp BS ID of the target anchor BS continues until the switchperiod has expired in step 117 or the Anchor BS Switch IE indicating afast switching cancel request to the target anchor BS is received fromthe serving anchor BS in step 113 even though the switch period has notexpired.

If it is determined in step 117 that the switch period has expired, theMS proceeds to step 119 where it determines whether CQICH allocationinformation to be used in the target anchor BS has been received fromthe serving anchor BS. Herein, the MS can be aware of the CQICHallocation information to be used in the target anchor BS through CQICHallocation information previously allocated before the MS performs afast switching operation from the serving anchor BS to the target anchorBS, or through Anchor BS Switch IE shown in Table 2 for the switchperiod. Alternatively, even in the process of adding a new active BS toit's the MS's diversity set, the MS can acquire CQICH allocationinformation of the active BS through a handover control message. Theoperation of managing the diversity set through the handover controlmessage will not be further described herein because it is not directlyrelated to the present invention.

If it is determined in step 119 that the CQICH allocation information tobe used in the target anchor BS has not been received, the MS proceedsto step 121 where it performs a fast switching operation from theserving anchor BS to the target anchor BS and then waits a preset time.Further, the MS determines whether CQICH allocation information isreceived through a MAP message broadcasted by the target anchor BSwithin the preset time. A format of CQICH allocation information, i.e.,CQICH Alloc IE, in the MAP message including the CQICH allocationinformation is shown in Table 3 below.

TABLE 3 Syntax Size Notes CQICH Alloc IE   CQICH ID Variable Index touniquely identify the CQICH resource assigned to the MS The size of thisfield is dependent on system parameter defined in DCD   Feedback 6 bitsIndex to the Fast feedback channel region channel offset marked by UIUC= 0   Period(p) 2 bits A CQI feedback is transmitted on the CQICH every2^(p) frames   Frame offset 3 bits The MS starts reporting at the frameof which the number has the same 3 LSB as the specified frame offset. Ifthe current frame is specified, the MS should start reporting in8frames.   Duration(d) 3 bits A CQI feedback is transmitted on the CQIchannels indexed by the CQICH ID for frames if d = 0, the CQICH isdeallocated if d = 111, the MS should report until the BS commend forthe MS to stop  }  } }

In Table 3, CQICH Alloc IE allocated in a target anchor BS indicatesCQICH allocation information used by an MS to exchange control signalswith the target anchor BS, and the CQICH Alloc IE includes CQICH ID,Feedback channel offset for providing actual location information of aCQICH in a CQI field defined in a UL-MAP message, and Frame offsetindicating a time at which the MS actually starts reporting a CQI valueafter being allocated a CQICH. In addition, the CQICH Alloc IE includesPeriod (p) indicating a period in which the MS reports the CQI value,and Duration (d) indicating an effective time for which the MS can usethe allocated CQICH.

If it is determined in step 121 that the CQICH allocation information isnot received, the MS proceeds to step 123. In step 123, the MS performsa network re-entry operation with the target anchor BS and then ends theprocess because it failed to receive CQICH allocation information fromthe target anchor BS, i.e., because the MS failed to be allocated theCQICH from the target anchor BS even after the MS completed a fastswitching operation from the serving anchor BS to the target anchor BS.Herein, the term “network re-entry operation” refers to an operation ofacquiring synchronization with the target anchor BS and then performinginitial ranging, registration and authentication.

However, if it is determined in step 119 that the CQICH allocationinformation to be used in the target anchor BS has been received, the MSproceeds to step 125. Also, if it is determined in step 121 that theCQICH allocation information has been received, the MS proceeds to step125. In step 125, the MS performs a fast switching operation andcommunication with the target anchor BS through the CQICH allocatedthereto, and then ends the process.

The FBSS-based fast switching operation of an MS in the conventionalIEEE 802.16 communication system has been described so far withreference to FIG. 1. Next, with reference to FIG. 2, a description willbe made of a format of an Anchor Switch Reporting (ASR) slot used in anFBSS-based fast switching operation of an MS in the general IEEE 802.16communication system.

FIG. 2 is a diagram illustrating a format of an ASR slot used in anFBSS-based fast switching operation of an MS in a conventional IEEE802.16 communication system. Reference numeral 201 representstransmission of a control signal from an MS to a serving anchor BS,shown on the time axis, reference numeral 203 represents transmission ofa control signal from the MS and a target anchor BS, also shown on thetime axis. As illustrated in FIG. 2, in the FBSS scheme, the time axisis divided in ASR slots. Each of the ASR slots is comprised of aplurality of, for example, M frames. The number, M, of framesconstituting the ASR slot is determined by a BS, and the MS obtains thenumber, M, of frames constituting the ASR, determined by the BS, througha DCD message.

Reference numeral 205 represents an ASR slot before a fast switchingoperation performed with the serving anchor BS by the MS, and referencenumerals 207 and 209 represent ASR slots in a switch period, for whichthe MS transmits a control signal used for informing the serving anchorBS of the fast switching operation from the serving anchor BS to thetarget anchor BS. The switch period includes one or more ASR slots. Thenumber of ASR sots constituting the switch period is also determined bythe BS, and the MS finds the number of ASR slots constituting the timeswitch, determined by the BS, through the DCD message. Reference numeral211 represents an ASR slot in which the MS performs communication withthe target anchor BS after performing a fast switching operation fromthe serving anchor BS to the target anchor BS, i.e., after completingthe switching operation.

In the ASR slot 205 before a fast switching operation, in which the MSis communicating with the serving anchor BS, the MS transmits a CQIvalue of the serving anchor BS to the serving anchor BS every frame inthe ASR slot 205 while performing communication with the serving anchorBS. In the ASR slot 205, if the MS determines that it should a performfast switching operation from the serving anchor BS to the target anchorBS, the MS waits until termination of the corresponding ASR slot, i.e.,the ASR slot 205, where it determined to perform the fast switchingoperation, instead of immediately performing the fast switchingoperation at the time where it determined to perform the fast switching.

After termination of the ASR slot 205, the MS informs the serving anchorBS for the switch period that it will perform fast switching from theserving anchor BS to the target anchor BS. In this case, the MStransmits, to the serving anchor BS, a CQI value C_(A) of the servinganchor BS and an indicator I_(B) indicating that it will perform a fastswitching operation from the serving anchor BS to the target anchor BS.Although the indicator I_(B) and the CQI value C_(A) are alternatelytransmitted in FIG. 2 on a frame-by-frame basis, by way of example, apattern for transmitting the indicators I_(B) and the CQI values C_(A)in the switch period can be variably determined by the MS. At any rate,the MS should transmit the indicator I_(B) and the CQI value C_(A) atleast once in a first ASR slot of the switch period.

After the end of the switch period, the MS that performed the fastswitching operation from the serving anchor BS to the target anchor BS,transmits a CQI value of the target anchor BS in the ASR slot 211 whileperforming communication with the target anchor BS.

As described above, in the FBSS scheme, the MS performs a fast switchingoperation from the serving anchor BS to the target anchor BS bytransmitting control signals using a CQICH. However, if the MS fails tobe previously allocated a CQICH from the target anchor BS afterperforming the fast switching operation from the serving anchor BS tothe target anchor BS in the switch period, the MS should perform networkre-entry with the target anchor BS as described above, causing a delayin connection setup.

If the MS fails to acquire CQICH allocation information from the targetanchor BS even after performing the FBSS-based fast switching operation,the MS performs a network re-entry operation with the target anchor BS,causing a connection setup delay. Accordingly, there is a need for ascheme capable of enabling the MS to rapidly set up a connection withthe target anchor BS after performing the FBSS-fast switching operation.

SUMMARY OF THE INVENTION

The present invention provides a system and method for allocating aCQICH in a communication system.

The present invention also provides a system and method for allocating aCQICH in an FBSS-based fast switching operation in a communicationsystem.

The present invention further provides a system and method in which anMS sends a CQICH allocation request to a target anchor BS in anFBSS-based fast switching process in a communication system.

According to an aspect of the present invention, there is provided amethod for requesting allocation of a Channel Quality InformationChannel (CQICH) by a Mobile Station (MS) in a communication system. Themethod includes: switching, by the MS, from a serving anchor BaseStation (BS) to a target anchor BS; detecting, by the MS, an absence ofa CQICH allocated from the target anchor BS; and transmitting, from theMS to the target anchor BS, a CQICH allocation request. The CQICHallocation request includes a CQICH allocation request header includinga basic Connection IDentifier (CID) of the MS and a Header CheckSequence (HCS) for the CQICH allocation request header.

According to an aspect of the present invention, there is provided amethod for receiving a Channel Quality Information Channel (CQICH)allocation request by a target anchor Base Station (BS) in acommunication system. The method includes: receiving, from a mobilestation (MS), the CQICH allocation request for allocating the CQICH tothe MS. The CQICH allocation request includes a CQICH allocation requestheader including a basic Connection IDentifier (CID) of the MS and aHeader Check Sequence (HCS) for the CQICH allocation request header.

According to an aspect of the present invention, there is provided asystem for requesting allocation of a Channel Quality InformationChannel (CQICH) in a communication system. The system includes a MobileStation (MS) for switching from a serving anchor Base Station (BS) to atarget anchor BS, detecting an absence of a CQICH allocated from thetarget anchor BS, and transmitting, to the target anchor BS, a CQICHallocation request. The CQICH allocation request comprises a CQICHallocation request header including a basic Connection IDentifier (CID)of the MS and a Header Check Sequence (HCS) for the CQICH allocationrequest header.

According to an aspect of the present invention, there is provided asystem for receiving a Channel Quality Information Channel (CQICH)allocation request in a communication system. The system includes atarget anchor Base Station (BS) for receiving the CQICH allocationrequest from a Mobile Station (MS). The CQICH allocation requestincludes a CQICH allocation request header including a basic ConnectionIDentifier (CID) of the MS and a Header Check Sequence (HCS) for theCQICH allocation request header.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a flowchart illustrating an FBSS-based fast switchingoperation of an MS in a conventional IEEE 802.16 communication system;

FIG. 2 is a diagram illustrating a format of an ASR slot used in anFBSS-based fast switching operation of an MS in a conventional IEEE802.16 communication system;

FIG. 3 is a flow diagram illustrating an FBSS-based fast switchingoperation in an IEEE 802.16 communication system according to anembodiment of the present invention;

FIG. 4 is a diagram illustrating a format of a Bandwidth Request headerfor requesting CQICH allocation according to an embodiment of thepresent invention; and

FIG. 5 is a flowchart illustrating an FBSS-based fast switchingoperation of an MS in an IEEE 802.16 communication system according toan embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention will now be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein has been omitted for clarity andconciseness.

The present invention proposes a system and method for allocating aChannel Quality Information Channel (CQICH) in a communication system.The present invention also proposes a system and method for allocating aCQICH in a Fast Base Station Switching (FBSS)-based fast switchingoperation in a Broadband Wireless Access (BWA) communication system. Inaddition, the present invention proposes a system and method, in whichif a mobile station (MS) fails to be allocated a CQICH from a targetanchor base station (BS) even after performing a fast switchingoperation from a serving anchor BS to the target anchor BS in a BWAcommunication system, the MS sends a CQICH allocation request to thetarget anchor BS and the target anchor BS allocates a CQICH to the MS inresponse to the CQICH allocation request from the MS. For convenience,an embodiment of the present invention will be described with referenceto an IEEE 802.16 communication system, one of the typical BWAcommunication systems. An embodiment of the present invention can alsobe applied to other communication systems as well as the IEEE 802.16communication system.

FIG. 3 is a flow diagram illustrating an FBSS-based fast switchingoperation in an IEEE 802.16 communication system according to anembodiment of the present invention. An MS 300 performs communicationwith a serving anchor BS 350 in step 301. Herein, the phrase the MS 300performs communication with a serving anchor BS 350 means thatallocation information for the MS 300 is included in MAP messages (i.e.,a downlink MAP (DL-MAP) message and an uplink MAP (UL-MAP) message),transmitted by the serving anchor BS 350. In the course of performingcommunication with the serving anchor BS 350, the MS 300 transmits a CQIvalue of the serving anchor BS 350 through a CQICH allocated from theserving anchor BS 350. Also, in the course of performing communicationwith the serving anchor BS 350, the MS 300 measures signal quality foreach of active BSs constituting its own diversity set in step 303.Herein, measuring the signal quality for each of the active BSs meansmeasuring strength, i.e., a carrier-to-interference and noise ratio(CINR) of a signal received from each of the active BSs.

The MS 300 determines to replace (switch) a serving anchor BS accordingto the signal quality measurement result for each of the active BSsincluded in the diversity set. In other words, the MS 300 determines toswitch its anchor BS from the serving anchor BS 350 to a particularactive BS among the active BSs (i.e., a target anchor BS 360), in step305. Herein, the MS 300 determines to switch its anchor BS from theserving anchor BS 350 to the target anchor BS 360 if there is any activeBS, i.e., the target anchor BS 360, having higher signal quality thanthat of the serving anchor BS 350.

Upon determining to switch its anchor BS, the MS 300 detects a startpoint of a switch period after termination of a corresponding AnchorSwitch Reporting (ASR) slot. In the switch period, the MS 300 transmitsa codeword mapped to a temporary BS indicator (Temp BS ID) of the targetanchor BS 360 to the serving anchor BS 350 in order to inform that theMS will perform a fast switching operation from the serving anchor BS350 to the target anchor BS 360, in step 307. A format of the ASR slotis to the same as the ASR slot format used in an FBSS-based fastswitching operation of an MS in the conventional IEEE 802.16communication system, described in connection with FIG. 2. Therefore, adetailed description thereof will be omitted herein for the sake ofclarity. Also, the codeword mapped to the Temp BS ID has been describedwith reference to FIG. 1 and will note be described further for the sakeof clarity.

After transmitting the codeword mapped to the Temp BS ID of the targetanchor BS 360 in the switch period, the MS 300 transmits a CQI value ofthe serving anchor BS 350 to the serving anchor BS 350 in step 309. Theoperation (steps 311 and 313) of transmitting a codeword mapped to aTemp BS ID of the target anchor BS 360 and transmitting a CQI value ofthe serving anchor BS 350 continues until the switch period expires oran Anchor BS Switch IE indicating a fast switching cancel request to thetarget anchor BS 360 is received from the serving anchor BS 350 eventhough the switch period has not expired. The Anchor BS Switch IE hasbeen described with reference to Table 2.

Even though the MS 300 transmitted the codeword mapped to the Temp BS IDof the target anchor BS 360 in the switch period to inform the servinganchor BS 350 that it will perform fast switching operation from theserving anchor BS 350 to the target anchor BS 360, the serving anchor BS350 may occasionally fail to recognize the scheduled fast switchingoperation in step 315. The serving anchor BS 350, because it failed todetect the scheduled fast switching operation of the MS 300 to thetarget anchor BS 360, cannot inform the target anchor BS 360 of thescheduled fast switching operation of the MS 300.

If the switch period expires, the MS 300 performs fast switching fromthe serving anchor BS 350 to the target anchor BS 360 in step 317. Afterperforming the fast switching to the target anchor BS 360, the MS 300recognizes in step 319 that it failed to be allocated a CQICH from thetarget anchor BS 360. Herein, the MS 300 detects allocation informationfor a CQICH allocated from the target anchor BS 360 through a MAPmessage broadcasted from the target anchor BS 360. If there is no CQICHallocation information for the MS 300 in the MAP message, the MS 300recognizes that it has failed to be allocated a CQICH from the targetanchor BS 360.

Upon recognizing the failure to be allocated a CQICH from the targetanchor BS 360, the MS 300 transmits a CQICH allocation request to thetarget anchor BS 360 in step 321. The MS 300 transmits the CQICHallocation request to the target anchor BS 360 by setting a Type fieldof a Bandwidth Request header to “111” before transmission. A format ofthe Bandwidth Request header transmitted for requesting CQICH allocationwill be described later in detail.

Upon receiving the Bandwidth Request header with Type field=“111” fromthe MS 300, the target anchor BS 360 recognizes in step 323 that itshould allocate a CQICH to the MS 300, determining that the MS requestsCQICH allocation. Therefore, the target anchor BS 360 allocates a CQICHto be used by the MS 300, and transmits information on the allocatedCQICH to the MS 300 in step 325. The CQICH allocation information, i.e.,CQICH Alloc IE, is broadcasted through a UL-MAP message, and a format ofthe CQICH Alloc IE has been described with reference to Table 3.

Although the operation of transmitting a CQICH allocation request of theMS 300 using the Bandwidth Request header has been described withreference to FIG. 3, the MS 300 can also transmit the CQICH allocationrequest in a method of adding Type/Length/Value (TLV) to aRanging-Request (RNG-REQ) message transmitted in the course ofperforming a network re-entry operation with the target anchor BS 360.That is, upon receiving the RNG-REQ message with a CQICH AllocationIndication bit being set in TLV thereof, the target anchor BS 360allocates a CQICH to the MS 300, determining that the MS 300 requestsCQICH allocation.

Although an embodiment of the present invention has been described withreference to the method of transmitting a CQICH allocation request ofthe MS 300 using the Bandwidth Request header, in alternate embodimentsit is also possible to define a new message or message header forrequesting CQICH allocation.

The FBSS-based fast switching operation in the IEEE 802.16 communicationsystem according to an embodiment of the present invention has beendescribed so far with reference to FIG. 3. Next, with reference to FIG.4, a description will be made of a format of a Bandwidth Request headerfor requesting CQICH allocation according to an embodiment of thepresent invention.

FIG. 4 is a diagram illustrating a format of a Bandwidth Request headerfor requesting CQICH allocation according to an embodiment of thepresent invention. The Bandwidth Request header is a Medium AccessControl (MAC) header transmitted by an MS to request allocation of abandwidth for transmitting a control signal or data, and a numeralwritten in each field of the Bandwidth Request header represents thenumber of bits constituting the corresponding field. A Header Type (HT)field of the Bandwidth Request header indicates a header type, and anEncryption Control (EC) field indicates encryption control. In addition,a Type field indicates a type of a MAC header, and a Bandwidth Request(BR) field indicates a requested bandwidth that the MS requests to beallocated. The Type field indicates a type of a corresponding bandwidthallocation request. For example, if the Type field is set to “000”, itmeans that the bandwidth allocation request indicates “incremental”.That is, it means that a value set later in the BR field indicates anadditional bandwidth that the MS requests to be allocated later. Forexample, if the Type field is set to ‘000’ and the BR field is set to“200” it means that the MS requests an additional 200-bit bandwidth tobe allocated thereto.

If the Type field is set to “001”, it means that the bandwidthallocation request indicates “aggregate”. That is, it means that a valueset later in the BR field indicates the needed total bandwidth that theMS was allocated. For example, if the Type field is set to “001” and theBR field is set to “800” it means that the MS is allocated an 800-bitbandwidth obtained by totaling the bandwidth allocated up to the presentand the bandwidth allocated through the bandwidth allocation request.

An embodiment of the present invention sets the Type field to “111”. Inthis case where the Type field is set to “111”, after performing a fastswitching operation from a serving anchor BS to a target anchor BS, anMS requests allocation of a CQICH to be used in the target anchor BS.When the Type field is set to “111”, the BR field can be filled with “0”(or Null), or filled with information related to a CQI value of thetarget anchor BS, measured by the MS. Herein, the information related tothe CQI value of the target anchor BS, measured by the MS, can beexpressed with, for example, 5 bits.

A Connection Identifier (CID) field of the Bandwidth Request headerindicates a basic CID of an MS, and a Header Check Sequence (HCS) fieldindicates a header check sequence. That is, the Bandwidth Request headeris a CQICH Allocation Request header used by the MS to request CQICHallocation.

The format of the Bandwidth Request header for requesting CQICHallocation according to an embodiment of the present invention has beendescribed so far with reference to FIG. 4. Next, with reference to FIG.5, a description will be made of an FBSS-based fast switching operationof an MS in an IEEE 802.16 communication system according to anembodiment of the present invention.

FIG. 5 is a flowchart illustrating an FBSS-based fast switchingoperation of an MS in an IEEE 802.16 communication system according toan embodiment of the present invention. Before a description of FIG. 5is given, it should be noted that a process of steps 501 through 519shown in FIG. 5 is substantially equal to the process of steps 101through 119 described with reference to FIG. 1, so a detaileddescription thereof will be omitted herein The MS determines in step 519whether CQICH allocation information to be used in the target anchor BShas been received from the serving anchor BS. If it is determined thatthe CQICH allocation information to be used in the target anchor BS hasnot been received, the MS proceeds to step 521 where it waits a presettime after performing a fast switching operation from the serving anchorBS to the target anchor BS, and then determines whether CQICH allocationinformation is received through a MAP message broadcasted by the targetanchor BS within the preset time. If it is determined in step 521 thatthe CQICH allocation information is not received, the MS proceeds tostep 523.

In step 523, the MS transmits a Bandwidth Request header for requestingCQICH allocation to the target anchor BS because the MS failed toreceive CQICH allocation information of the target anchor BS, i.e.,because the MS failed to be allocated a CQICH from the target anchor BSeven after completing a fast switching operation from the serving anchorBS to the target anchor BS. The MS determines in step 525 whether thenumber of transmissions for the Bandwidth Request header is greater thanthe predetermined maximum number of transmissions. If the number oftransmissions for the Bandwidth Request header is not greater than themaximum number of transmissions, the MS returns to step 521.

However, if it is determined in step 525 that the number oftransmissions for the Bandwidth Request header is greater than themaximum number of transmissions, the MS proceeds to step 527 where itperforms a network re-entry operation with the target anchor BS and thenends the process. Herein, the term “network re-entry operation” refersto an operation of acquiring synchronization with the target anchor BSand then performing initial ranging, registration and authentication.

If it is determined in step 519 that the CQICH allocation information tobe used in the target anchor BS has been received, the MS proceeds tostep 529. Also, if it is determined in step 521 that the CQICHallocation information has been received, the MS proceeds to step 529.In step 529, the MS performs communication with the target anchor BSthrough a CQICH allocated thereto, and then ends the process.

As can be understood from the foregoing description, in the BWAcommunication system according to an embodiment of the presentinvention, during FBSS-based fast switching, an MS sends a CQICHallocation request to a target anchor BS if the MS fails to be allocateda CQICH from the target anchor BS even after performing fast switchingfrom a serving anchor BS to the target anchor BS, thereby contributingto a reduction in connection setup delay. In particular, for fastswitching, the MS sends the CQICH allocation request to the targetanchor BS using a Bandwidth Request header, enabling fast connectionsetup to the target anchor BS.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

1. A method for requesting allocation of a Channel Quality InformationChannel (CQICH) by a Mobile Station (MS) in a communication system, themethod comprising: switching, by the MS, from a serving anchor BaseStation (BS) to a target anchor BS; detecting, by the MS, an absence ofa CQICH allocated from the target anchor BS; and transmitting, from theMS to the target anchor BS, a CQICH allocation request, wherein theCQICH allocation request includes a CQICH allocation request headerincluding a basic Connection IDentifier (CID) of the MS and a HeaderCheck Sequence (HCS) for the CQICH allocation request header.
 2. Themethod of claim 1, wherein the CQICH allocation request header is aMedium Access Control (MAC) header having a predetermined type.
 3. Themethod of claim 1, wherein the CQICH allocation request header includesChannel Quality Information (CQI) of the target anchor BS.
 4. The methodof claim 1, wherein detecting the absence of the CQICH allocated fromthe target anchor BS comprises: monitoring, by the MS, a MAP messagereceived from the target anchor BS for CQICH allocation from the targetanchor BS; and detecting, by the MS, the absence of the CQICH allocatedfrom the target anchor BS, when there is no CQICH allocation informationincluded in the MAP message.
 5. A method for receiving a Channel QualityInformation Channel (CQICH) allocation request by a target anchor BaseStation (BS) in a communication system, the method comprising:receiving, from a mobile station (MS), the CQICH allocation request forallocating the CQICH to the MS, wherein the CQICH allocation requestincludes a CQICH allocation request header including a basic ConnectionIDentifier (CID) of the MS and a Header Check Sequence (HCS) for theCQICH allocation request header.
 6. The method of claim 5, wherein theCQICH allocation request header is a Medium Access Control (MAC) headerhaving a predetermined type.
 7. The method of claim 5, wherein the CQICHallocation request header includes Channel Quality Information (CQI) ofthe target anchor BS.
 8. The method of claim 5, further comprising:determining, by the target anchor BS, to allocate the CQICH to the MS;and allocating, by the target anchor BS, the CQICH to the MS.
 9. Themethod of claim 8, further comprising: transmitting, by the targetanchor BS, allocation information for the CQICH to the MS.
 10. Anapparatus for requesting allocation of a Channel Quality InformationCHannel (CQICH) in a Mobile Station (MS) of a communication system, theapparatus comprising: a processor for detecting an absence of a CQICHallocated from a target anchor Base Station (BS) after switching from aserving anchor BS to the target anchor BS; and a transmitter fortransmitting, to the target anchor BS, a CQICH allocation request forallocating a CQICH, wherein the CQICH allocation request is a CQICHallocation request header including a basic Connection IDentifier (CID)of the MS and a Header Check Sequence (HCS) for the CQICH allocationrequest header, from the MS to the target anchor BS, for requestingallocation of the CQICH.
 11. The apparatus of claim 10, wherein theCQICH allocation request header is a Medium Access Control (MAC) headerhaving a predetermined type.
 12. The apparatus of claim 10, wherein theCQICH allocation request header includes Channel Quality Information(CQI) of the target anchor BS.
 13. The apparatus of claim 10, whereinthe processor monitors a MAP message received from the target anchor BS,waits for CQICH allocation from the target anchor BS, and detects theabsence of the CQICH allocated from the target anchor BS when there isno CQICH allocation information in the MAP message.
 14. An apparatus forreceiving a Channel Quality Information CHannel (CQICH) allocationrequest for allocating a CQICH in a target anchor Base Station (BS) of acommunication system, the apparatus comprising: a receiver for receivingthe CQICH allocation request for allocating the CQICH from a MobileStation (MS); and a processor for detecting a need to allocate a CQICHaccording to the CQICH allocation request, wherein the CQICH allocationrequest is a CQICH allocation request header including a basicConnection IDentifier (CID) of the MS and a Header Check Sequence (HCS)for the CQICH allocation request header, from the MS to the targetanchor BS, for requesting allocation of the CQICH.
 15. The apparatus ofclaim 14, wherein the CQICH allocation request header is a Medium AccessControl (MAC) header having a predetermined type.
 16. The apparatus ofclaim 14, wherein the CQICH allocation request header includes ChannelQuality Information (CQI) of the target anchor BS.
 17. The apparatus ofclaim 14, wherein the processor allocates the CQICH to the MS.
 18. Theapparatus of claim 17, further comprising: a transmitter fortransmitting allocation information for the CQICH to the MS.